A white LED light emitting apparatus recently getting the limelight as a lighting, an LCD backlight, an automobile light, and the like, commonly includes an LED light emitting device emitting blue or near ultraviolet light and a phosphor transforming wavelengths into visible light by using the emitted light from the light emitting device as an excitation source.
In one method for realizing the white LED, a blue light emitting diode using InGaN-based material having a wavelength of 450 to 550 nm is used as a light emitting device, and a yellow light emitting YAG-based phosphor represented by the empirical formula of (Y,Gd)3(Al,Ga)5O12 is used as a phosphor.
In the white LED, the blue light emitted from the light emitting device is incident to a phosphor layer, and absorption and reflection of the light are repeated for several times by the phosphor layer. The absorbed blue light by the phosphor may be transformed into yellow light. The transformed yellow light and a portion of the incident blue light are mixed and appreciated as white light through the eyes of a viewer.
However, the white LED having the above-described structure includes a small amount of red component in the light, has a high color temperature, and lacks of red and green components. Thus, only lightings having deteriorated color rendering properties may be obtained.
In addition, an oxide-based phosphor generally tends to decrease light intensity when the wavelength of the excitation source exceeds 400 nm. In this case, a highly luminescent white light may not be obtained by using the blue light.
Accordingly, an oxynitride-based phosphor having stability better or equal to that of the oxide phosphor and having a good light emitting efficiency at an excitation source exceeding 400 nm attracts much concern in the white LED field, recently. In addition, since the oxynitride-based phosphor has been originally developed as engineering ceramics, the efficiency decrease and color change due to humidity and heat are small.
However, the presence of the oxynitride-based phosphor in a component region deviated from a-type or R-type sialon (Si—Al—O—N) is little known.